Field of the Invention
The present invention relates to an image projection apparatus such as a projector, and particularly to an image projection apparatus using a semiconductor light-emitting element as a light source.
Description of the Related Art
An image projection apparatus using, as a light source, a semiconductor light-emitting element such as an LED or a semiconductor laser requires using multiple semiconductor light-emitting elements in order to project an image having a sufficient brightness. However, the semiconductor light-emitting element has a characteristic in which its light emission quantity (luminance) and its main light emission wavelength are fluctuated depending on its temperature, an operating environment temperature, a driving current for light emission and the like. For this reason, when the multiple semiconductor light-emitting elements are used, variations in the above fluctuation of the individual semiconductor light-emitting elements results in luminance unevenness in the projected image and influences on colors in the projected image.
Japanese Patent Laid-Open No. 2012-155268 discloses, as a method to be used for a light source unit including multiple semiconductor light-emitting elements, a method of providing temperature sensors at multiple positions in a cooling path, classifying the light-emitting elements on a basis of detection results of the sensors and controlling light quantities (light emission intensities) of the light-emitting elements. Japanese Patent Laid-Open No. 2008-003270 discloses a method of providing a light separation portion to a condenser lens disposed between a color combination optical system and a rod integrator, causing part of an illumination light to exit from the light separation portion to outside of an effective area, providing a detection element that detects an intensity of the exiting light, and controlling light quantities of light-emitting elements on a basis of a detection result of the detection element.
However, the method disclosed in Japanese Patent Laid-Open No. 2012-155268 requires, when number of the semiconductor light-emitting elements is increased to provide a higher luminance, increasing number of the temperature sensors in order to detect a temperature distribution in the light source unit with high accuracy.
On the other hand, the method disclosed in Japanese Patent Laid-Open No. 2008-003270 requires an optical component to constitute the light separation portion, which results in an increase in size of the apparatus. Furthermore, the apparatus uses the part of the illumination light to detect the light quantity of the light-emitting element, which results in an inevitable decrease in a brightness of the projected image.